Brominated epoxy polymers as wood coating flame retardant formulations

ABSTRACT

The present invention discloses novel flame retardant aqueous formulations comprising micronized particles of brominated epoxy polymers having a predetermined molecular weight, their use as flame retardant coating of wood-based substrates, their preparation and flame-retarded wood-based substrates prepared by using them.

This application is a Divisional of U.S. application Ser. No. 16/012,251filed Jun. 19, 2018, (now U.S. Pat. No. 10,626,289), which is aContinuation-in-Part of U.S. application Ser. No. 14/917,694 filed Mar.9, 2016, (now U.S. Pat. No. 10,533,278), which is the U.S. nationalphase of International Application No. PCT/IL2014/050807 filed Sep. 11,2014 which designated the U.S. and claims the benefit of U.S.Provisional Application No. 61/876,783 filed Sep. 12, 2013, the entirecontents of each of which are hereby incorporated by reference.

The present invention relates to the field of flame-retardants and, moreparticularly, to flame retardant coatings, paints, composites andadhesives, their preparation and efficacy (flame retardancy) in thefinal applications.

Coatings are an essential part of everyday life both in decorative andfunctional applications. Consequently, coating flammability is a seriousindustrial concern.

In recent years, polymers have become more attractive and preferred asflame retardant (FR) agents over small molecules, due to their lowbiological penetration into cells, and thus epoxy polymers can be used.

Epoxy polymers or epoxy resins, also known as polyepoxides are a classof reactive prepolymers and polymers which contain epoxide groups. Epoxyresins may be reacted (cross-linked) either with themselves throughcatalytic homopolymerization, or with a wide range of co-reactantsincluding polyfunctional amines, acids (and acid anhydrides), phenols,alcohols, and thiols. These co-reactants are often referred to ashardeners or curatives, and the cross-linking reaction is commonlyreferred to as curing. Reaction of polyepoxides with themselves or withpolyfunctional hardeners forms a thermosetting polymer, often withstrong mechanical properties as well as high temperature and chemicalresistance. Epoxy polymers have a wide range of applications, includingmetal coatings, use in electronics/electrical components, high tensionelectrical insulators, fiber-reinforced plastic materials, andstructural adhesives.

Brominated epoxy polymers are known as flame retardants in the plasticindustry and are prepared by melting during the preparation of thethermoplastic material fiber. Some examples are listed below:

US20060266986 (to Rhodia) discloses flame retardant yarns and textilesand the process of obtaining them from a thermoplastic matrix, wherebyat least one flame-retardant agent is deposited in the threads, fibersand/or filaments during the extrusion production. Among thethermoplastic matrixes disclosed therein are, inter alia, brominatedepoxy oligomers.

In another example, EP728798 (to Sumitomo Chemical Company) disclosesthe preparation of flame retardant thermoplastic polyester resincomposition. In particular, it discloses the melting together(melt-kneading) of an impact-resistance improver (A) and of aflame-retardant (B), whereas component B may be, among other options,bromine-containing flame retarders such as brominated epoxy oligomer.

In yet another example, WO2001007500 (by the present applicant)discloses a flame retardant compound for use with thermoplastic resins,which is a halogenated epoxy resin, having its epoxy groups blocked atleast partially by halogenated bisphenol monoalkyl ether (HBPMAE).

In a further example, WO2004108826 (to DOW) discloses a curable flameretardant epoxy resin composition including (a) at least one flameretardant epoxy resin; (b) at least one amphiphilic block copolymer, and(c) a curing agent wherein the flame retardant epoxy resin can be abrominated epoxy resin.

However, as noted in all of the examples above, brominated epoxypolymers have never been proposed for wood-coating applications, whichhave different requirements compared to extrusion and plasticapplications.

Lately, in WO2015036998 to some of the inventors, brominated epoxypolymers were successfully formulated for textile finishingapplications. Among other requirements, in textile coating applicationsthe flame retardant must be dispersible in aqueous media, must providedispersions that are stable for 6 months or more, must be compatiblewith waterborne adhesive emulsions such as latex or polyacrylates, mustprovide flame retardancy at dry add-ons of less than 50% of thesubstrate self-weight, must yield a flexible, translucent, continuousand non-flaking coating, must provide a coating that is durable tolaundry and must be non-leaching from the coating film.

In light of the desirable properties of said textile-suitable flameretardant formulations based on brominated epoxy polymers, it would beof great advantage to harness these transparent, stable, aqueousdispersions, which are compatible with waterborne adhesive emulsionssuch as latex or polyacrylates for coating of other materials other thanfabric, such as wood. Wood surfaces are desirable substrates to be flameretarded, particularly if the flame retarded substrate maintains itsoriginal appearance after the coating application on its surface.However, in the case of wood surface coating, distinct requirementswhich mainly relate to the physical adsorption of the advantageous flameretardant to the coated wood surface need to be met in order to allow ahomogeneous and efficient coating. There are known flame retardantcoatings suitable for wood surfaces in the field, for example,US20080280036 (to Cal-West Specialty Coatings) discloses a peelableprotective coating based on vinyl acetate—ethylene or vinyl—acrylicemulsions with a flame retardant, mostly intumescent. Applications overlaminated or painted wood, inter alia, are disclosed. Easy peel-off isnot a desired property of a permanent coating. As a further example,U.S. Pat. No. 5,296,306 (to Great Lakes Chemical Corp.) disclosesgrafting brominated monomers into styrenic and acrylic latexes, anddemonstrates good adhesion, inter alia, to wood. The process is morecumbersome and rigid than blending a flame retardant with a suitablelatex. Additionally. U.S. Pat. No. 3,877,974 (to White Chemical Corp)discloses coating flammable materials, mainly textile but also plywood,with a flame retardant coating comprising a brominated compound, metaloxide and a high molecular weight binder. Plywood coated withtetrabromophthalic anhydride and arsenic trioxide 1-2 μm particles, in10:1 parts of vinyl acetate—ethyl acrylate binder with ca 5:1 parts oftitanium dioxide pigment demonstrated self-extinguishing properties. Itshould be noted, however, that the disclosed wood coating formulationcontains tetrabromophthalic anhydride, a low-molecular-weight compound,which as explained above is less favorable in terms of penetration intocells, arsenic trioxide which is highly toxic, and because of the highload of titanium dioxide, the coating is assumed to be non-transparentdue to the amount of pigment in said formulation.

Thus, there remains a need to find aqueous dispersions, which yieldtransparent coating and are suitable as flame retardants for wood. Thepresent invention discloses the successful preparation of stable andefficient brominated epoxy polymer-based aqueous dispersions, which canbe easily applied to wood surfaces, giving rise to homogeneoustransparent flame retardant coatings.

The present invention illustrates the successful preparation ofbrominated flame retardant formulations which are suitable andadvantageous for wood coating applications, giving rise to atransparent, homogeneous and easy to apply flame retardant coating.

Therefore, according to one aspect of the invention, there is nowprovided a flame retardant formulation, comprising at least onebrominated flame retardant and at least one binding agent which aresuitable for wood coating, in the form of an aqueous dispersion,comprising micronized particles of at least one brominated epoxy polymerand an aqueous carrier.

As can be seen from Examples 1-6 herein below, aqueous dispersionscomprising micronized particles of at least one brominated epoxy polymerdemonstrated effective flame retardant properties while exhibitinghomogeneity and transparency when applied to wood. The wood-basedsubstrate sought to be coated with said aqueous dispersions requires ahigher binder content than the amount which is needed, for example, fortextile applications. This requirement stems from the fact that in manycases of wood-based materials, the main use is as a surface coatingwhich demands higher amount of binder in order to form a uniformcoating, in contrast, for example, to some textile applications whereinthe flame retardant material can sometimes be directly incorporated intothe textile fibers. As used herein, the term “binding agent” refers to apolymeric component of a formulation used to form a coating on thedesired surface, e.g. wood surface. Unless the context clearly dictatesotherwise, the term may be interchangeably used with “latex”, “paintlatex”, “resin”, “polymer resin” and the like.

Therefore, in one aspect, the present invention provides a flameretardant formulation suitable for a wood-based substrate, in the formof an aqueous dispersion, comprising micronized particles of at leastone brominated epoxy polymer having a molecular weight ranging from1,000 to 5,000 grams/mol, water, and at least one binding agent, andfurther comprising at least one additive selected from the groupconsisting of a dispersing agent, a flame retardant synergist, asmoldering suppressant agent, a surface active agent, an antifoamingagent, a preservative, a stabilizing agent, a thickening agent, awetting agent, a suspending agent, a pH buffer, a hardener, a curingagent, a sequestering agent, a detergent, a dye, a pigment, and anymixture thereof. In some embodiments, the formulation as described abovecomprises a single binding agent. In some embodiments, the binding agentis selected from the group consisting of acrylate-based agents,urethane-based agents, alkyd-based agent resin, saturated polyesterbased agent resin, epoxy-based resin, and on the like. In some relatedembodiments, said binding agent is an acrylate-based agent which isself-crosslinking agent.

According to some embodiments, the formulation as described abovecomprises said at least one brominated epoxy polymer in an amountranging from 7% to 30% by weight. In some other embodiments, the totalamount of solids within the formulation is ranging from 25-60% byweight.

According to the principles of the present invention, end-cappedbrominated epoxy of the form 2,4,6-tribromophenyl end-cappedtetrabromobisphenol, also known by the name bis(2,4,6-tribromophenylether)-terminated tetrabromobisphenol A- epichlorohydrin resin, as shownby Formula (I) below:

wherein n indicates the degree of polymerization (for example, withweight average molecular weight from 700 to 20,000, e.g., 700-3000), caneffectively reduce the flammability of coated wood-based substrate. Insome embodiments, the brominated epoxy polymer micronized particles havea size distribution of a d₅₀<5 micron, a d₉₀<10 micron and a d₉₀<30micron. The compounds of the Formula I may be obtained commercially, orprepared as known in the art.

In some embodiments, the brominated epoxy polymer is characterized byhaving Tg lower than 160° C., preferably lower than 140° C. and evenlower than 130° C.

The term “micronized particles” refers to particles having an averageparticle size of about 10 microns or less in size. A range from about 1to 10 microns is contemplated with a range of about 1 to 5 micronspreferred with a range of about 1 to 3 microns especially preferred. Themicronized particles may be prepared from particles greater than 10microns in size by using milling techniques known in the art such as wetmilling or dry milling. Thus, as used herein, the term “micronizedparticles” may be interchangeably used with the term “milled particles”or “milled brominated epoxy polymers”.

The term “epoxy polymers” may be interchangeably used with the term“epoxy resins” or “polyepoxides” or epoxy prepolymers” or the like, asis known to a person skilled in the art, and generally refer to reactiveprepolymers and polymers which contain epoxide groups.

The term “brominated epoxy polymers” refers to epoxy polymers containingwithin the repeating unit at least one bromine group. The polymers mayor may not also be end-capped with bromine-containing groups.

As used herein and in the claims, the term “aqueous dispersion” isinterchangeable with the term “latex” and is understood to mean, for thepurposes of the present invention, the dispersion of polymer in anaqueous carrier, such as water. The aqueous dispersion is usuallycharacterized by a concentration of solids ranging from 25-60%. Thesolid content includes all the components of the formulations that arenot the aqueous carrier, such as the flame-retardant (FR), binder,dispersing agent, flame retardant synergist, smoldering suppressionagent, wetting agent, thickener etc.

As the formulations as described herein may be useful as transparentpaints over wood surfaces of an object, the term “substrate” and theterm “wood substrate” are used interchangeably herein, unless thecontext clearly dictates otherwise should be construed either as awooden surface of an article, or an article having a surface made ofwood.

As explained hereinabove, in order to obtain the formulations describedherein, it has been found that the brominated epoxy polymer shouldpreferably be ground to a pre-determined size to provide particleshaving a size which is suitable to enable an effective flame retardationof wood.

Thus, the coarse brominated epoxy polymer particles need to first bemicronized before they can be used in the formation of the aqueousdispersions of the present invention. The particles may be micronized bya variety of milling techniques as known in the art, and include bothdry milling and wet milling, as detailed further below, of the coarsebrominated epoxy polymers particles.

The coarse brominated epoxy polymers particles are typicallycharacterized by an upper “cut-off” of the particle size (largestparticle size) which is about 300 microns, preferably a cut-off rangingfrom about 300 microns to about 270 microns and/or by a d₉₉ ranging fromabout 275 microns to about 100 microns and/or by a d₉₀ ranging fromabout 160 microns to about 60 microns and/or by a d₅₀ ranging from about44 microns to about 22 microns.

The micronized particles of the present invention, obtainable by drymilling or wet milling of the brominated epoxy polymer coarse particlesdescribed above, are characterized by a “cut-off” of the particle sizewhich is lower than 35 microns and by a d₉₉ which is lower than 30microns, preferably lower than 25 microns and even lower than 20microns. Yet preferably, the d₉₉ ranges from about 20 microns to about15 microns, more preferably the d₉₉ ranges from about 15 microns toabout 7 microns.

Furthermore, the micronized particles of the present invention arecharacterized by a d₉₀ which is lower than 10 microns. Preferably, thed₉₀ ranges from about 10 microns to about 7.5 microns, more preferablythe d₉₀ is lower than 7.5 microns, and ranges from about 7.5 microns toabout 5 microns.

Yet further, the micronized particles of the present invention arecharacterized by a d₅₀ which is lower than 5 microns. Preferably, thed₅₀ ranges from about 5 microns to about 3 microns, more preferably thed₅₀ is lower than 3.5 microns and ranges from about 3.5 microns to about3 microns.

Thus, according to preferred embodiments of the invention, the particlesize of at least 99% of the milled brominated epoxy polymer particles(d₉₉) is smaller than about 30 microns, more preferably smaller than 20microns. According to additional preferred embodiments of the invention,the particle size of at least 90% of the milled brominated epoxy polymerparticles (d₉₀) is smaller than about 10 microns, more preferablysmaller than 7.5 microns. According to yet additional preferredembodiments of the invention, the particle size of at least 50% of themilled brominated epoxy polymer particles (d₅₀) is smaller than about 5microns, more preferably smaller than 3.5 microns. According to anotherpreferred embodiment of the invention, the milled brominated epoxypolymers need to be milled to have a size distribution of d₅₀<5 micronand a d₉₀<10 micron and a d₉₉<30 micron, more preferably of d₅₀<3.5micron, a d₉₀<7.5 micron and a d₉₉<15 micron.

According to the principles of the present invention, the formulationmust comprise at least one binder in order to form a homogenous filmhaving efficient adhesion of the milled brominated epoxy-based flameretardant to the wood-based substrate. Thus, in some embodiments, the atleast one binding agent utilized in the formulation as described aboveis in an amount ranging from 35% to 85% by weight. In some embodiments,the binder is a self-crosslinking polymer, e.g. self-crosslinkingacrylic polymer. In some exemplary embodiments, the self-crosslinkingacrylic polymers comprise Alberdingk AC 2523. Alberdingk AC 2019, DOWPRIMAL IW 3311, DOW PRIMAL AC-261 and the like. In some otherembodiments, the binder is a polyurethane polymer. In some furtherexemplary embodiments, the polyurethane polymers comprise Alberdingk U180 VP, Alberdingk® U 9600 VP. Alberdingk® PUR-MATT 340 VP and the like.In further related embodiments, antimony oxide flame retardant synergistis optionally present in the formulation. In a closely relatedembodiment, the molar ratio between antimony and bromine (Sb:Br) rangesfrom 1:3 to 1:18. In yet some other embodiments, a dispersing agent inan amount of up to 5% wt is present in the formulation as describedabove.

In some other embodiments, the formulation as described above comprisesa wetting agent and/or a thickening agent in an amount of up to 5% byweight each.

In another aspect, the present invention further provides a process forthe preparation of the flame retardant formulation for wood substrate ofthe invention comprising: a) Obtaining coarse particles of at least onebrominated epoxy polymer having a molecular weight ranging from 1,000 to5,000 grams/mol; b) milling said coarse particles to obtain micronizedparticles having a size distribution of d₅₀<5 micron and a d₉₀<10 micronand a d₉₉<30 micron; c) preparing an aqueous solution comprising anaqueous carrier, coalescing agent and a dispersing agent; d) adding saidmicronized particles to said aqueous solution, and mixing said solutionto obtain a mixed aqueous dispersion and optionally adding a thickeningagent; and e) adding to said mixed aqueous dispersion a binder andoptionally adding a smoldering suppression agent and/or a wetting agentand/or a synergist, and mixing said dispersion.

In some embodiments, the preparation process as described above maycomprise an additional step, in which at least one additive selectedfrom the group consisting of a surface active agent, an antifoamingagent, a preservative, a stabilizing agent, a suspending agent, a pHbuffer, a hardener, a curing agent, a sequestering agent, a detergent, adye, a pigment and any mixture thereof is added.

In a further aspect, the present invention provides a process forobtaining a flame retarded wood-based substrate, said process comprisingapplying the flame retardant formulation as described above to aflammable wooden surface. In some embodiments, applying the flameretardant formulation onto the wood-based substrate is affected by meansof brushing, spreading, coating, dipping, printing, or spraying. In someembodiments, the application of the flame retardant formulation onto thewood-based substrate takes place at room temperature. Without beingbound by theory or mechanism of action, it was demonstrated that theformation of a flame retardant film—which constitutes the flameretardant coating on top of the wooden surface, may occur at bothelevated and reduced temperatures, i.e. above freezing temperature, andthat the film formation is not limited to room temperature. However, forthe purposes of easy application of said formulation, it would be mostconvenient to apply the formulation at room temperature and avoid theneed to, e.g. warm up the surface in order to induce the flame retardantcoating formation. The formulation may be characterized by a particularrheological behavior. For the ease of application, the formulation mayhave a dynamic viscosity of between 3000 and 100 cp, at speed of between0.3 and 100 rpm, measured at 25° C.

In yet another aspect, the present invention provides a flame retardedwood-based substrate having a homogeneous flame retardant film thereon,said film comprising micronized particles of the at least one brominatedepoxy polymer as described above, crosslinked on said wood-basedsubstrate, wherein: a) said brominated epoxy polymer has a molecularweight ranging from 1,000 to 5,000 grams/mol; b) said micronizedparticles have a size distribution of d₅₀<5 micron, d₉₀<10 micron andd₉₀<30 micron; c) said wood-based substrate comprises a binding agent inan amount of at least 35% by weight; and e) said wood-based substrateoptionally further comprises at least one additive selected from thegroup consisting of a flame retardant synergist, a smolderingsuppressant agent, a surface active agent, an antifoaming agent, apreservative, a stabilizing agent, a thickening agent, a dispersingagent, a wetting agent, a suspending agent, a pH buffer, a hardener, acuring agent, a sequestering agent, a detergent, a dye, a pigment andany mixture thereof. In some currently preferred embodiments, said filmis transparent.

As appear herein and in the claims, the term “transparent” refers to aproperty of the film coating the wooden substrate. The meaning oftransparent coating as it appears in this application refers to the factthat the texture and/or the wooden color can still be easily observed inthe final coated wooden substrate. The term “translucent” as used hereinand in the claims refers to a film which is transparent—meaning thewooden color can be seen through the coating of the invention to someextent, while giving rise to a coated substrate having a mat finishing.The transparency of the film of the invention can be measured usingDATACOLOR 650, as described in Example 7. The transparent film of theinvention is characterized by having transparency values of betweenabout 30% to about 90% as measured by DATACOLOR 650. In some embodimentthe transparency values are between 40%-80% as measured by DATACOLOR650. In some other embodiments, the transparency values are between45%-75% as measured by DATACOLOR 650.

In a closely related embodiment, the flame retarded wood-based substratehaving the flame retardant film thereon displays its original woodencolor. In some embodiments, the original wooden color presents in a matfinishing due to the translucent flame retardant coating of theinvention. In another embodiment, the flammable wood-based substrate onwhich the flame retardant coating of the invention is applied to, can bea natural wood substrate, engineered wood and any combination thereof.For example, the wooden substrate may be, but is not limited to, oak,pine, plywood, beech, cherry, and the like.

FIGURES

The following figures depict the results of flammability tests carriedout in a cone calorimeter as described in Example 4.

FIG. 1: depicts the heat emission of samples 1 to 6.

FIG. 2: depicts the smoke emission of samples 1 to 6.

FIG. 3: presents calculated calorimetric parameters of samples 1 to 6.

EXAMPLES

Materials and Methods

Brominated Flame Retardant Polymer

TexFRon®4002 (2,2′-[(1-Methylethylidene)bis[(2,6-dibromo-4,l-phenylene)-oxymethylene]]-bisoxirane polymer with2,2′,6,6′-tetrabromo-4,4′-isopropylidenediphenol and2,4,6-tribromophenol. CAS #135229-48-0).

FR1410 used for comparative Example 6 Decabromodiphenyl ethane, CAS84852-53-9.

Resins

Acrylic based resins: Alberdingk® AC 2523 (47-49% solids, Minimum FilmFormation Temperature (MFFT) 0° C.), Alberdingk® AC 2019 (45-47% solids,MFFT 17° C.), Primal™ IW-3311 (41% solids. MFFT 42° C.), polyurethanebased resin: Alberdingk® U9600 VP (34-36% solids, MFFT 0° C.);

Auxiliary Additives

BYK-093: defoamer reagent, contains a mixture of foam-destroyingpolysiloxanes and hydrophobic solids in polyglycol, was obtained fromBYK-Chemie GmbH.

BYK-346: wetting agent, a solution of a polyether-modified polysiloxanewas obtained from BYK-Chemie GmbH.

BYK-420: thickening agent and anti-settling agent, a solution of amodified urea obtained from BYK-Chemie GmbH.

BYK-2010: wetting and dispersing agent, structured acrylate copolymerwith pigment affinic groups obtained from BYK-Chemie GmbH.

Tafigel® PUR 45: thickening agent, non-ionic polyurethane in butyltriglycol/water was obtained from Munzing Chemie GmbH.

PG—propylene glycol coalescing agent obtained from Gadot Chemicals.

Rheolate® 212: thickening agent promoting improved flow of water-basedsystems, polyether polyurethane based resin in water was obtained fromElementis specialties.

Antimony pentoxide (APO)—flame retardant synergist was obtained fromNyacol Nano Technologies, Inc.

Flammability Tests:

The cone calorimeter and the NFPA 701 vertical burn tests were used forquantitative flammability analysis of the formulations set forth above.Cone calorimeter analysis was conducted in order to evaluate theflammability of the compositions prepared. Data was collected by thecone calorimeter under a heat flux of 50 kW/m², and specimen separationof 25 mm. The parameters which were investigated were the ignition time,heat release rate (HRR), total heat release (THR) and the HRR peak.

NFPA 701: a method for assessing the propagation of flame in varioustextiles and films under specified fire test conditions. In this test, ahanging substrate under testing, (plywood was used) was exposed to a 10cm flame for 45 seconds. After said 45 seconds, the flame wasautomatically put out, while the flame which was caught by the testedsubstrate was monitored until it was auto-extinguished, and the durationof said auto-extinguishing was reported in seconds. In the measurementscarried out for the present invention, a sample that did not demonstrateauto-extinguishing properties (burned completely) under the testconditions as described above, was reported as “fail”.

Cone calorimetry: a fire testing tool based on the principle that theamount of heat released from a burning sample is directly related to theamount of oxygen consumed during the combustion. Briefly, in the conecalorimeter, a radiant heat is projected onto a sample before ignitionand during burning of the sample, and several parameters, such as timeto ignition and the heat release profile of the tested sample aremeasured. The amount of heat a material generates is directly correlatedwith the severity of a fire, such as fire growth rate. The cone gathersdata regarding the ignition time, mass loss, combustion products, heatrelease rate and other parameters associated with its burningproperties.

Example 1—Preparation of Micronized Particles

Preparation of micronized end-capped brominated epoxy TexFRon® 4002(2,2′-[(1-Methylethylidene)bis[(2,6-dibromo-4,1-phenylene)oxymethylene]]bisoxiranepolymer with 2,2′,6,6′-tetrabromo-4,4′-isopropylidenediphenol and2,4,6-tribromophenol, CAS #135229-48-0). TexFRon® 4002 was micronized bya Micronizer Jet Mill (dry milling). The particle size distributionbefore and after the milling was measured using Malvern Mastersizer 2000in water (3 minutes ultrasonic treatment, 500 psi, 1250 rpm).

Example 2—Preparation of TexFRon® 4002 Aqueous Dispersions—Premix 4002

TexFRon 4002 (66 grams) having a size distribution of d₅₀<5 microns,d₉₀<10 microns, d₉₉<30 microns, was added to a mixed solution containingdeionized water (84.8 grams), Disperbyk-2010 (5 grams), BYK-093 (1 g)and propylene glycol (42 g) using a dissolver stirrer (R 1303 Dissolverstirrer IKA with EUROSTAR power control-visc motor, IKA) at a rate of600 RPM. The dispersion was allowed to mix for 10 minutes. Followingsaid mixing, BYK 420 (1.2 g) was added slowly to the mixture and wasleft to stir for another 30 minutes, producing 200 gr TexFRon 4002remix. Table 1 describes the premix composition in terms of percent byweight:

TABLE 1 Ingredient wt % Water 42.4 PG 21 BYK-2010 2.5 BYK-093 0.5 Flameretardant (TexFRon 4002) 33 BYK-420 0.6

The viscosity of TexFRon 4002 premix was measured in Brookfield DVIIviscometer, equipped with spindle S63, and gave rise to the followingvalues: 2499 cp at 0.3 rpm, 177 cp at 60 rpm, and 158 cp at 100 rpm;this pseudoplastic behavior is highly desirable for paint applications.

Example 3

A. The preparation of different wood coating formulations comprisingTexFRon® 4002 was carried out in two consecutive steps, including thepreparation of the water dispersion TexFRon 4002 premix following theprocedure described above in Example 2, and mixing said premix with thefollowing ingredients as follows:

For the preparation of formulation comprising 15 wt % TexFRon 4002,Alberdingk 2523 AC (102.4 g), BYK 093 (1.6 g), BYK 346 (0.6 g) andDisperBYK-2010 (2 g) were added during stirring in a dissolver stirrer(R 1303 Dissolver stirrer IKA with EUROSTAR power control-vise motor,IKA) at a rate of 400 RPM. After 10 minutes of mixing, TexFRon 4002premix (92.4 g) was added during stirring with increased stirring rateof 600 rpm, followed by the addition of Rheolate-212 to form 200 gr ofstable acrylic fire retardant coating.

For formulations comprising Antimony Pentoxide dispersion, the latterwas slowly added after Rheolate-212 in the last stage followed byadditional 10 minutes stirring.

Several coating formulations were prepared as detailed in Table 2,utilizing the preparation procedure as described above, and varying inTexFRon 4002 premix and resin (Alberdingk AC-2523) content as describedin Table 2 herein below in terms of percent by weight.

B. Sample preparation: the formulations obtained as described in step Awere applied onto plywood boards (30*15*0.3 cm) and pine wood samples(10*10*1 cm) utilizing paint brush (3 layers, with intervals of at least4 hours to allow drying) on both sides of the board at room temperature.The resultant coatings appeared to have a mat finishing and the originalcolor of the wood samples was observed. The plywood samples were usedfor the NFPA testing and the pine samples were used for the conecalorimeter testing.

The solids fraction (% solids) in the formulations which appeared inTable 2 was measured by Loss On Drying (LOD) HR-Halogen (MettlerToledo). The sample was applied on aluminum plate and was heated to120′C. The weight loss was measured after getting stable weight, thesolid fraction was calculated according to the following: 100%−LOD=%solids in formulation

The coated plywood substrates were examined under NFPA 701 testingconditions as described above and the auto-extinguishing time wasrecorded per each coating formulation as summarized in Table 2:

TABLE 2 Sample number 1 2 3 4 5 6 Sample name 15 wt % 15 wt % 10 wt % 10wt % 5 wt % 2.5 wt % TexFRon TexFRon TexFRon TexFRon TexFRon TexFRon4200 4200 + APO 4200 4200 + APO 4200 + APO 4200 + APO Alberdingk 51.239.59 67.4 59.86 78.63 88.02 AC 2523 (wt %) APO (wt %) — 11.61 — 7.543.77 1.88 BYK-093 (wt %) 0.8 0.8 0.8 0.8 0.8 0.8 BYK-346 (wt %) 0.3 0.30.3 0.3 0.3 0.3 BYK-2010 (wt %) 1 1 1 1 1 1 Premix-4002 (wt %) 46.2 46.230 30 15 7.5 Rheolate-212 (wt %) 0.5 0.5 0.5 0.5 0.5 0.5 NFPA 701 (sec)9.03 3.23 55.4 2.27 fail fail % solids (measured) 40.8 40.7 46.5 43.544.4 47.1

According to Table 2, it can be seen that samples comprising less than10 wt % TexFRon 4002 in their coating formulation failed in the burningtest—and were totally burned. Additionally, sample number 3, having 10wt % TexFRon 4002 which was APO-free, took a long time toauto-extinguish (55.4 seconds) while a similar sample having 10 wt %TexFRon 4002 and containing APO demonstrated a much shorterauto-extinguishing time (2.27 seconds). This later effect of APOpresence was consistent also in the samples comprising 15 wt % TexFRon4002 (samples 1 and 2), where APO appeared to shorten the time needed inorder to achieve an auto-extinguished sample.

Example 4

Flammability measurements according to ASTM E1354 standard were carriedout utilizing cone calorimeter Stanton Redcroft. The heat release ofcoated 100 mm×100 mm×10 mm plywood samples were measured, using heatflux of 50 kW/m² and Specimen Separation of 25 mm.

Calculated values: 1) Smoke parameter: Peak heat release*SEA*10⁻³ (SEAis specific extinction area m² kg⁻¹). 2) Fire performance index: Time ofignition/peak heat release rate

Heat emission measurement of the samples prepared according to Table 2are depicted in FIG. 1. According to FIG. 1, APO containing samples 2and 4 having 15 and 10 wt % TexFRon 4002, respectively, demonstrated alower peak heat release rate than corresponding samples 3 and 5, whichwere APO-free. According to FIG. 2, similar samples in terms ofbrominated epoxy flame retardant content demonstrated similar smokerelease values with and without APO. According to FIG. 3, the overallfire performance index demonstrated a higher flame performance index forAPO-containing samples 2 and 4, having 15 and 10 wt % TexFRon 4002,respectively, in comparison to corresponding samples 3 and 5, which wereAPO-free. Additionally, it was noted that an increase in the flameretardant content within the sample appears to result mostly in anincrease in the fire performance index.

Example 5

APO-free wood coating formulations comprising 15% TexFRon 4200 andvarying resins were prepared as described in Example 3, by replacingAlberdingk AC-2523 with the desired resin in each formulation asindicated in Table 3 herein below. The obtained formulations wereapplied onto plywood boards as described hereinabove. The differentAPO-free coating formulations and their corresponding NFPA testingresults are summarized in Table 3:

TABLE 3 DOW Alberdingk Alberdingk Alberdingk Primal AC 2523 AC 2019U9600 VP IW-3311 Resin (wt %) 51.2 51.2 53.2 53.2 BYK-093 0.8 0.8 — —(wt %) BYK-346 0.3 0.3  0.3  0.3 (wt %) BYK-2010 1 1 — — (wt %)Premix-4002 46.2 46.2 46.2 46.2 (wt %) Rheolate-212 0.5 0.5 — — (wt %)Tafigel PUR 45 — —  0.3  0.3 (wt %) NFPA 701 (sec) 9.03 33.4 22.8  9.55% solids 40 39 34   37   (calculated)

According to Table 3, Alberdingk AC-2523 acrylic resin yielded the bestresults in terms of shortest time to achieve an auto-extinguishedsample.

Example 6

A comparative example between the wood coating formulations of theinvention which are based on TexFRon 4002 flame retardant and woodcoating formulations based on the known flame retardant FR-1410(reference samples) was carried out in the following manner: two coatingformulations having 15 wt % flame retardant material and two coatingformulations having 10 wt % flame retardant material where prepared foreach flame retardant (TexFRon 4002 and FR-1410) as described in Example3. One of each coating formulation was APO-free and the other had APOadditive therein according to Table 4:

TABLE 4 15% TexFRon 15% TexFRon 15% FR- 15% FR- 10% TexFRon 10% TexFRon10% FR- 10% FR- 4200 4200 + APO 1410 1410 + APO 4200 4200 + APO 14101410 + APO Alberdingk 51.2 39.59 51.5 34.2 67.4 59.86 67.4 56.4 AC 2523(wt %) APO (wt %) — 11.61 — 17 — 7.54 — 11 BYK-093 (wt %) 0.8 0.8 0.80.8 0.8 0.8 0.8 0.8 BYK-346 (wt %) 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3BYK-2010 (wt %) 1 1 1 1 1 1 1 1 ***FR Premix 46.2 46.2 45.9 46.2 30 3030 30 (wt %) Rheolate-212 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 (wt %) NFPA701 (sec) 9.03 3.23 8.91 3.95 55.4 2.27 fail 2.7 ***The premixcomposition used for FR-1410 was prepared according to the proceduredescribed in Example 2, only utilizing FR-1410 instead of TexFRon 4002as the main flame retardant.

-   -   ***The premix composition used for FR-1410 was prepared        according to the procedure described in Example 2, only        utilizing FR-1410 instead of TexFRon 4002 as the main flame        retardant.

The wood boards coated with formulations based on FR-1410 appeared whitein comparison to the wood boards coated with TexFRon 4002 basedformulations, which appeared to maintain the original wood color as aresult of the transparent coating which was formed.

According to Table 4 it can be seen that for both flame retardants(FR-1410 and TexFRon 4002) the presence of APO within the coatingimproved the auto-extinguishing time of the samples. Additionally, itwas demonstrated, that in the presence of APO, TexFRon 4002 formulationswere shown to be superior to FR-1410 formulations in terms ofauto-extinguishing time of the corresponding samples.

-   -   An additional parameter that was demonstrated is the wood        appearance after the coating. The wooden sample coated with        FR-1410 appeared to be white in comparison to the wooden sample        coated with TexFRon 4002. This advantage of the flame retardant        coating of the invention is achieved even though the particle        size distribution of the FR-1410 is similar to the particle size        distribution of TexFRon 4002. It should be noted that the solid        wt % was similar for both FR-1410 and TexFRon 4002 formulations.

Example 7

Paint formulation was applied on glass using an applicator (byko-driveby BYK) with 10 cm Film Casting Knife (BYK) forming a 300 micron wetfilm. After 24 h the dry film was pulled-off from the glass and wasanalyzed for transparency using DATACOLOR 650 (by DATACOLOR). Thetransparency properties of the flame retardant coating of the inventionare detailed in Table 5:

TABLE 5 Sample Transparency (%) 99.45% Alberdingk acrylic resin (AC2523) + 99.38 0.25% Byk 346 + 0.3% Tafigel 45 68.8% Alberdingk acrylicresin (AC 2523) + 46.5 30.2% TexFRon 4002 premix + 0.66% Byk 346 + 0.34%Tafigel 45

As can be seen from the transparency measurement, the original color ofthe wooden sample was visible, the coating which included the flameretardant therein appeared to be translucent, giving rise to a matfinishing of the wooden sample.

The invention claimed is:
 1. A flame retarded wood-based substratehaving a homogeneous flame retardant film thereon, said film comprisingmicronized particles of brominated epoxy polymer according to Formula I,

wherein n indicates the degree of polymerization having a molecularweight ranging from 1,000 to 5,000 grams/mol; attached to the surface ofsaid wood-based substrate, wherein: said micronized particles have asize distribution of d50<5 micron, d90<10 micron and d99<30 micron; saidhomogenous flame retardant film comprises a binding agent in an amountof at least 35% by weight; and said homogenous flame retardant filmoptionally further comprises at least one additive selected from thegroup consisting of a flame retardant synergist, a smolderingsuppressant agent, a surface active agent, an antifoaming agent, apreservative, a stabilizing agent, a thickening agent, a dispersingagent, a wetting agent, a suspending agent, a pH buffer, a hardener, acuring agent, a sequestering agent, a detergent, a dye, a pigment andany mixture thereof.
 2. The flame retarded wood-based substrate of claim1, wherein said film is transparent.
 3. The flame retarded wood-basedsubstrate of claim 1, wherein said wood-based substrate displays itsoriginal color.
 4. The flame retarded wood-based substrate of claim 1,having an “after flame” time ranging from 0 seconds to 10 seconds. 5.The flame retarded wood-based substrate of claim 1, wherein saidflammable wood-based substrate is a natural wood substrate or anengineered wood and any combination thereof.